1. Field of the Invention
The present invention relates to a plate member for use as a material of light shielding blade members which are required to move at a high velocity, such as focal plane shutter blades or lens shutter blades of a camera.
2. Related Background Art
In general, it is desirable to operate a light-shielding blade at a high velocity with a small force, and with minimal flexing of the blade. This requires a light-shielding blade that is lightweight and that possesses high strength and rigidity.
To meet the foregoing requirement, a plate member for use as a material of light-shielding blades has been proposed which has a laminate construction including a reinforced-resin intermediate layer composed of a resin matrix with uni-directionally oriented continuous (long) carbon fibers, and reinforced-resin surface layers composed of a resin matrix with continuous carbon fibers uni-directionally oriented in a direction substantially orthogonal to the direction of the fibers in the intermediate layer, the light-shielding member having a total thickness of 60 to 120.mu.. This type of plate member is disclosed, for example, in Japanese Patent Application Laid-Open No. 59-61827 U.S. Pat. No. 4,482,231, Japanese Patent Application Laid-Open No. 62-199439 and Japanese Patent Application Laid-Open No. 63-17435.
Obviously, the layers forming this plate member are arranged in plane-symmetry in the thickness direction. In addition, each of the intermediate and surface layers may be a laminate layer composed of a plurality of thin reinforced resin sheets. In general, 20 to 50 blades are formed by cutting or punching from this plate member, such that, in each blade the longitudinal direction of the carbon fibers of the intermediate layer is substantially orthogonal to the longitudinal axis of the blade. The light-shielding blades thus formed are lightweight and superior in hardness and rigidity, and are actually used in cameras having a high shutter release speed of 1/8000 second.
The light-shielding blade thus formed suffers from disadvantages due to its small thickness which usually ranges between 60 and 120.mu.. The first problem is that the plate member as the blank of the light-shielding blade generally exhibits a large thickness variation. The second problem is that the plate member is inferior in flatness, i.e., that the plate member is warped or distorted. The third problem is that the light-shielding blade formed by punching or cutting also is inferior in flatness.
FIG. 1 is an illustration of a vertical-running type focal plane shutter in assembled state, wherein the light-shielding blades formed by the above-described process are used as a first blade 31, a second blade 39, a third blade 40, a fourth blade 41 and a fifth blade 42.
Arms 34 and 35 are rotatably connected to pins 32, 33 provided on the first blade 31. The arms 34, 35 are rotatable about shafts 37, 38 provided on a shutter base plate 36. The pins 32, 33 and the shafts 37, 38 are arranged in a parallelepiped quadrilateral form, so that the first blade 31 translationally moves in the vertical direction of the aperture 46 in accordance with rotation of the arms 32, 33. However, the second blade 39, the third blade 40, the fourth blade 41 and the fifth blade 42 are moved in a manner different from that of movement of the first blade 31. More specifically, a pin 43 provided on the first blade 31 is rotatably connected to the second blade 39, while a pin 45 provided on an arm 44 rotatably supported by a shaft 37 engages with a cam groove 39a formed in the base portion of the second blade 39. Consequently, the motion of the second blade 39 is determined by the movement of the pin 45 and the contour of the cam groove 39a, through the action of the pin 43. The third blade 40 is rotatably carried by the shaft 38 and a cam groove 40a engaging with the pin 45 is provided on the base portion thereof. The fourth and fifth blades 41 and 42 are also rotatably carried by the shaft 38 and are provided with cam grooves 41a and 42a for engagement with the pin 45. The pin 45 also is rotatably connected to arm 34 which is rotatably supported by the shaft 37, so as to rotate together with the arm 44 which rotates about the shaft 37. The cam grooves 39a, 40a, 41a, and 42a are arranged such that the blades are developed to cover the aperture 46 when the first blade 31 is positioned above the aperture 46 as viewed in the Figure, whereas, when the first blade 31 is retracted to the underside of the aperture 46, all the blades are superposed. In this arrangement, the third to fifth blades 40 to 42 rotate about the center of the shaft 38 as if forming a fan or a sector. In general, a focal plane shutter device of the kind described includes a pair of the described group of blades. One of the blade groups serves as shutter opening blades, while the other serves as shutter closing blades.
The focal plane shutter device of the kind described, employing blades made from the conventional plate member,tends to suffer from problems in regard to connection between the driving system and the blades due to inferior flatness of the plate member and due to local reductions in strength caused by presence of micro-cracks and cavities in the plate material. In addition, the appearance of the blades and applicability of DL (dry lubricant) are also impaired.